1. Field of the Invention
The invention concerns anti-jack-knifing apparatus for articulated vehicles, primarily for tractor-type vehicles and articulated buses or coaches; hereafter, for simplicity, the driven and towed units of the articulated vehicle will be referred to as "tractor" and "trailer".
2. Discussion of the Prior Art
Anti-jack-knifing devices are known which exert a braking moment around a king-pin, that articulates a tractor and a trailer together, against the moment of forces tending to cause jack-knifing of the tractor when the tractor or the trailer is braked. Thus for instance British Pat. No. 1,256,947 discloses anti-jack-knifing apparatus wherein the braking moment is provided by a disc brake comprising a plurality of plates. The stationary part of the brake is fixed to the base or rubbing plate of the trailer while the rotary part is connected with the king-pin.
In deviation from conventional constructions, the king-pin is not fixed rigidly to the rubbing surface of the trailer, but instead has a tongue which fits into an appropriately formed part of the coupling on the tractor and thus rotates with the tractor. The plates of the brake are clamped together by a compressed air-operated piston. The air supply is taken from the emergency air brake system of the trailer and is controlled by a special valve which is built into the air brake system of the trailer.
In another known construction disclosed in British Pat. No. 1,240,554 the anti-jack-knifing brake device is located at the steered front shaft of the trailer and is operated by a brake chamber connected with the brake system of the trailer.
In the construction known from British Pat. No. 1,295,045, the anti-jack-knifing device includes pistons for a disc brake which also receive pressure from the wheel brake system of the vehicle, but only when a predetermined pressure in the brake system of the vehicle has been exceeded.
In the construction disclosed in British Pat. No. 1,243,005 the anti-jack-knifing brake device is installed in the trailer and is air-operated. A special valve, controlled by wheel slip sensing means, permits air to pass from a tank into the brake system.
The main disadvantage of the above-mentioned known constructions, except for that of the above-mentioned British Pat. No. 1,243,005, is that the control of the anti-jack-knifing braking system is coupled to the operation of the braking system of the vehicle. These known control systems start from the premise that the lateral supporting force of the tires decreases and thus the possibility of jack-knifing arises when the wheels at the rear tractor shaft lock on breaking.
However, there is no necessary logical connection between braking locking and jack-knifing, since there can be factors other than wheel locking to cause a decrease or elimination of the lateral support forces on the tires mounted on the rear shaft, and if jack-knifing results from a circumstance other than braking, the known anti-jack-knifing devices are ineffective.
In the known devices, the anti-jack-knifing brake construction exerts a braking force the magnitude of which depends on the controlling pressure of the brake valve. In this way the upper limit of the braking effort that can be exerted is limited since the anti-jack-knifing braking construction is unable to render the articulated vehicle rigid when braking occurs during the negotiation of a bend.